Thermal switch

ABSTRACT

A double-point, thermally-responsive, switch assembly for a self-cleaning electric baking oven fulfills several functions. The switch assembly includes a tube-rod type of differential thermal expansion thermostat which serves to translate a rise in temperature into rectilinear motion, which is translated through a ball and socket joint to a motion amplifier lever. The lever in turn effects the opening and closing of a pair of switches. One switch serves as an over-temperature limit protection for use during the normal baking cycle to effect cutting of power to the baking elements in the event of failure of the primary control system. A second switch is of the double-throw type which is used during the self-cleaning cycle. It serves first to close a first set of contacts to provide power for a cooling fan for keeping the outer wall temperatures of the oven within safe temperature limits. A second set of contacts, upon opening, removes power from a circuit which provides an electroresponsive means such that, when the temperature within the oven cavity is above a predetermined level, the oven door may not be opened. Means are provided for calibrating or adjusting the temperature at which each of the switches will be caused to be switched.

United States Patent [1 owling [11] 3,821,683 5] June 28, 1974 1 THERMALSWITCH [75] Inventor: Teamus Bowling, Fern Creek, Ky.

[73] Assignee: General Electric Company,

Louisville, Ky.

22 Filed: Apr. 17,1973 [21] App1.No.:3511,848

Primary Examiner-Harold Broome Attorney, Agent, or Firm-Richard L.Caslin; Francis H. Boos [5 7] ABSTRACT A double-point,thermally-responsive, switch assembly for a self-cleaning electricbaking oven fulfills several functions. The switch assembly includes atube-rod type of differential thermal expansion thermostat which servesto translate a rise in temperature into rectilinear motion, which istranslated through a ball and socket joint to a motion amplifier lever.The lever in turn effects the opening and closing of a pair of switches.One switch serves as an, over-temperature limit protection for useduring the normal baking cycle to effect cutting of power to the bakingelements in the event of failure of the primary control system. A secondswitch is of the double-throw type which is used during theself-cleaning cycle. It serves first to close a first set of contacts toprovide power for a cooling fan for keeping the outer wall temperaturesof the oven within safe temperature limits. A second set of contacts,upon opening, removes power from a circuit which provides anelectroresponsive means such that, when the temperature within the ovencavity is above a predetermined level, the oven door may not be opened.Means are provided for calibrating or adjusting the temperature at whicheach of the switches will be caused to be switched.

110 Claims, 5 Drawing Figures 3e 9 90 2e 8 12 L9 22 7 er a4. 80/ v14-THERMAL SWITCH BACKGROUND OF THE INVENTION The present invention relatesto a thermallyresponsive switch assembly, and more particularly, to adouble-point, thermally-responsive, safety control switch assembly for aself-cleaning electric oven to serve as a redundant switch to removepower from the oven heating units in case of a failure of the main ovencontrol thermostat, and further to effect the operation of an indicatorlamp and a cooling fan to maintain safe operating temperatures of theouter surfaces of the oven, and further to interrupt a door interlockcircuit to prevent the opening of the oven door when the temperaturewithin the oven is above a predetermined level.

This invention is related to the art of self-cleaning ovens whichutilize a pyrolytic method of cleaning the interior walls of the ovencavity of food soil by raising the temperature of the walls into aheat-cleaning temperature range above about 750F. At this hightemperature, the food soils are transformed into gaseous degradationproducts which are then oxidized and finally discharged from the ovencavity. The details of this method and of a preferred embodiment of anoven design in which it may be carried out are fully disclosed in US.Pat. No. 3,121,158 of Bohdan Hurko, which is assigned to the sameassignee as the present invention.

Thermally-responsive or thermostatic switches are commonly used indomestic appliances such as baking ovens. Perhaps one of the most commontypes is the hydraulic thermostat which is essentially a hydraulicfilledbellows or diaphragm assembly that converts volumetric expansion orcontraction thereof into rectilinear motion acting upon a switchmechanism. Others are of the differential thermal expansion type, andmore particularly of the tube and rod thermostat type which control themovement of a lever in order to open and close separate switchingelements. Such devices commonly use a lever with a fulcrum at one of itsends, the rod of the tube and rod thermostat applying pressure near thisfulcrum point to effect movement in switching at the other end of thelever. Others couple the rod through a slip friction device to thelever. Still others use a tube-rod thermostat having its rod connectedto a lever in tension, the lever having its fulcrum at one end and itsswitching contact at the other end. The prior art has also shown the useof ball and socket joints in compression to interconnect the rod of thetube-rod thermostat with the drive lever.

The present invention is concerned with the functions; firstly ofinsuring that during the baking operation, the over air temperature doesnot rise above the 600-650F range in the event of a failure of one ofthe temperature control elements; secondly of insuring that thehousewife may not unlatch the oven door during a heat-cleaning operationunless the air temperature returns below approximately 550F; thirdly ofinsuring that the outside wall temperatures of the oven do not reachcertain unsafe temperatures, and to effect this, at approximately 540F,a cooling fan is switched on to cause air to be circulated between theinner and outer walls of the oven.

The principal object of the present invention is to provide adouble-point, thermally-responsive switch assembly which operates inconjunction with the oven heating means to back up the normal or primaryoven thermostatic control system to prevent an overtemperature conditionin the event of a control failure in the primary oven thermostat system.

It is a further object to provide a double-point, thermally-responsiveswitch assembly which has differential expansion thermostat which cantranslate a rise in temperature into rectilinear motion which will betranslated to a motion amplifier lever and in turn to a pair ofswitches, one of which serves as a safety means to deactivate a loadcircuit during an over-temperature condition in the normal bakeoperation, and the other of which is a double function switch for useduring the self-cleaning cycle first to activate a first control circuitand then to deactivate another control circuit when the temperaturebeing monitored is above a predetermined level.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided a multiple point, thermally-responsive switch assemblycomprising a base, a housing attached to the base, and a plurality ofswitch means attached to the housing. Hingedly attached to the base isrigid, motion amplifier means which is adapted to operationally engagethe switch means. Temperature responsive means is attached to the base,and has a driver which is operationally coupled with the amplifier meansby a universal motion translator, the driver and the amplifier meansbeing coupled in tension to effect opening and closing of the switchmeans upon the temperatureresponsive means being exposed topredetermined temperatures.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. l is an elevational view, broken away to reveal the variouscomponents of the switch assembly of the present invention, in one formthereof;

FIG. 2 is a rear elevational view of the housing of the switch assembly;

FIG. 3 is a view much like FIG. 1, however, taken along the lines 3-3 ofFIG. 2 to further expose the operating components of the switchassembly;

FIG. 4 is an interior view taken generally along the lines l-4 of FIG. 1to show the relation of the motionamplifier lever with the switcheslocated within the housing; and

FIG. 5 is a schematic representation of a power and control circuituseful for a self-cleaning electric oven embodying thethermally-responsive switch assembly of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I of thedrawing, there is illustrated in accordance with the present invention,a doublepoint, thermally-responsive, control switch assembly as for usewith a self-cleaning electric oven. A housing such as electricallyinsulating housing 12 of phenolic resin or the like is formedsubstantially in the shape of a hollow box. The housing 112 is furnishedwith a base or metallic cover 14 for substantially closing the housingand providing a mounting structure for certain components of the switchassembly. Cover plate 14 is held in place by a series of fasteningscrews (not shown) arranged in the holes as shown at 16 in FIG. 2.

Attached to the cover 14 is a temperature responsive means such asdifferential expansion tube-rod thermostat 20 intended to be exposed tothe operating temperatures of the oven interior. Theremostat 20comprises an outer tube 22 affixed to cover 14 at 24 by suitable means(such as welding). A driver, such as inner rod driver 26, is secured tothe crimped free end 28 of outer tube 22 by suitable means (as bywelding). Driver 26 is formed of a material such as Rodar or the like,having a coefficient of thermal expansion which is much lower than thatof the material of outer tube 22. Tube 22 is formed of a material, suchas lnconel or the like, having a coefficient of thermal expansion whichis relatively high or large.

Pivotally or hingedly attached to cover 14 by hinge pin 32 is a rigid,motion-amplifier means such as metallic motion-amplifier lever 34. As isshown, driver 26 of thermostat 20 projects loosely through an opening incover plate 14, and further, through an opening in motion-amplifierlever 34, and has been provided with threads 36 at its free end. Motionis transferred from the driver 26 to lever 34 through a universalmotiontranslator such as ball and socket joint motiontranslator 40. Thisjoint is formed of a recess or socket formed in lever 34 and is shownmore clearly in FIG. 3 as at 42. The ball portion is formed on one sideof a nut 44 which is threadedly engaged with rod driver 26. Compressivebias means, such as compression spring 48, is disposed between lever 34and cover 14 for maintaining socket 42 of the lever in positive contactwith motion translator ball 44. Spring 48 engages lever 34 at one endthereof adjacent motiontranslator 40 and is fixedly attached to cover 14through holes provided therein.

Mounted within housing 12 are switch means, including a first switch 50shown in FIG. 1. First switch 50 is of the normally-closed, single-pole,single-throw type, and further of the high-current type having aswitchblade 51 adapted to flex only at the support or hinge point 52 toopen a set of contacts 54, 54'. Compressive bias means, such ascompression spring 56, is provided for maintaining contact points 54, 54in tightly closed engagement to prevent their destruction or weldingtogether as by arcing or overheating. Referring to FIG. 3, a secondswitch 60 of the single-pole, double-throw, rocker-arm type is providedsecuredly attached within housing 12. Switch 60 has a rocker arm 61,first normally-open contacts 62, 62 and second normallyclosed contacts64, 64'. This switch 60 is also provided with compressive bias means,such as compression spring 66, for maintaining the normally-closedcontacts in tightly closed engagement, and further, for maintaining inthe open position the normally-open contacts.

Referring to FIG. 2, there is shown the rear side of housing 12 toreveal the external electrical connections or terminals of switches 50and 60. Terminals 72 and 74 correspond to first switch 50, and extendinto housing 112 to form part of the mounting means of first switch 50.Terminals 76, 78 and 80 correspond to second switch 60 and pass throughhousing 12 to form the mounting means and part of the contact means ofswitch 60.

As shown in FIGS. 1 and 3, motion-amplifier lever 34 has a protrusion orabutment 84 formed of electrically insulating material, such as phenolicor the like. This abutment is securedly attached to the lever 34, andserves to operationally engage switches 50 and 60 at suitable points onswitch blade SI and rocker arm 61 respectively to effect switching inresponse to thermostat 20 being subjected to predetermined temperaturelevels. Another relationship may be seen of this engagement of abutment84 with switches 50 and 60 by referring to FIG. 4. As is shown, switches50 and 60 are suitably located within housing 12 so as to be responsiveto movement or contact by abutment 84 and thereby by lever 34.Switchblade 51 is suitably fastened to terminal 72 as by spot welding at85 so as to be hinged that it may be flexed at hinge point 52 inresponse to engagement by abutment 84. This has been accomplished byproviding rolled over edges on switch blade 51 for the whole lengththereof except at the hinge point 52. By providing a rigid switch bladeand allowing flexing only at the hinge point, and in conjunction withcompressive spring 56 applying pressure against the switch blade 51 tomaintain it in its normally closed position, the problem of change incalibration of opening temperature of contacts 54, 54' due to flexing,softening or work-hardening of the lever arm of switch blade 51 isessentially obviated. Contacts 54, 54' will maintain their relativepositions during their lifetimes.

As can also be seen in FIG. 4, second switch 60 has a rocker arm 61which is maintained in position by Center terminal 78. An elongated slot86 in FIG. 3 (not readily visible) is provided in the inner portion ofterminal 78 such that rocker arm 61 is free to move within the slot 86(right to left in FIG. 3) subject to pressure from abutment 84. Theinitial effect then of increased pressure from abutment 84 is to causenormally-open contact 62, 62' to close, while at the same time allowingnormally-closed contracts 64, 64' to remain closed. As the oven cavitytemperature to which thermostat 20 is subjected is elevated, furtherpressure by abutment 84 will, after a dwell period ofa few degreesFarcnheit, force normally-closed contracts 64, 64' to open, while stillmaintaining the then closed contacts 62, 62 in a closed position. Itshould be noticed that rocker arm 61 is always in electrical contactwith terminal 78 mainly through the connections and structure of a dual,hairpin spring 66.

Referring now to FIGS. 2 and 3, calibration means are provided foradjusting the temperature at which switches 50 and 60 will be caused tobe switched by motion-amplifier lever 34 and thereby by the thermostat20. One such adjustment is the combination of the threaded end 36 ofthermostat driver rod 26 and the ball nut 44 and socketmotion-translator 40. An opening 90 is provided in the rear wall ofhousing 12 through which adjustment may be made of ball nut 44 so as tocalibrate the point corresponding to the temperature at which it isdesired that contacts 54, 54' of first switch 50 will be caused to beopened by abutment 84 of lever 34. Further, a set screw 92 is providedwhich is threadedly engaged with the inner end of terminal 80 of secondswitch 60 so as to form the contact 62. An opening 94 is provided in therear wall of housing 12 such that set screw 92 may be adjustedexternally, as by a screwdriver, to calibrate the point corresponding tothe temperature to which thermostat 20 is subjected at which it isdesired that normally-open contacts 62, 62' will become closed inresponse to contact by abutment 84.

Thermally-responsive switch assembly W has been primarily designed foruse in a domestic or household baking oven of the self-cleaning type.Thermostat 20 has been designed to project within the cavity of the ovenso as to be reponsive to operating temperatures therein. As shown inFIG. 1, mounting means 98 are provided for securing the switch assemblyto a wall of the oven.

Preferably an opening is provided in the rear wall of the oven linersuch that thermostat 20 may project through for a total distance ofapproximately 7 inches, flange 98 serving as part of the mounting means,coming to rest against the oven wall surface. Also included in themounting means is a heat sealing gasket and a mounting washer (neitherof which is shown) which will serve to compressibly hold flange 9Ssecurely against the oven wall and which will be fastened thereto bysuitable means (such as by screws, not shown).

The double-point, thermally-responsive switch assembly 10 is designed tobe used as a control compo nent for a self-cleaning electric oven whosepower and control circuits are illustrated in the schematic diagram ofFIG. 5. The oven is furnished with an electrical service of 3-wireEdison source of power; nominally of 240 volts, single phase, 60 Hz.,A.C. which is usually available in the average residence having adequatewiring. This voltage source is fed to the oven through a 3- wire cablehaving a pair of line wires L, and L with a voltage of 240 voltstherebetween, and a grounded neutral conductor N, for supplying theelectrical load of the oven. This electrical load is characterized bythree heating elements; a baking element MN), 21 broiling element lltl2and a mullion heater 104. The bake element 100 is usually locatedadjacent the bottom wall of the oven, the broil element 102 is usuallylocated adjacent the top wall of the oven and the mullion heater 104 isusually wrapped around the outside of the oven liner adjacent to thefront opening for replenishing the heat lost through and around the dooropening during a high temperature, heat-cleaning or pyrolytic cycle.These heating elements W0, W2 and 1041 are arranged in circuits incombination with an oven selector switch 106 for setting up differentcombinations of heating elements at different voltages to obtain avariety of heating rates. A manually settable oven thermostat 1108 isalso provided for controlling the temperature within the oven atpreselected temperatures during baking operations and a maximumtemperature during oven cleaning operations. Such an oven thermostat T08is arranged serially with the heating elements lltlt), 102 and 1M foropening and closing the power circuit to the heating elements as afunction of oven temperature with relation to the temperaturepredetermined or preset by the thermostat 108.

The oven selector switch 106 is provided with a series of line inputterminals denoted as Ll, N, Lll, and L2, as well as a series of loadterminals denoted as K, J, and P. This selector switch 106 is providedwith a plurality of switch contacts 112 through 120. These switchcontacts are labeled with the particular cooking or cleaning operationthat is involved when such contacts are closed. For example, during aBaking or a Time Baking operation, contacts H2, H3, MS and 1119 areclosed. During a Broiling operation, contacts 116 and ill! are closed.During a Cleaning cycle, contacts 113, llM, 1115, H6, H9 and 1120 areclosed.

The Baking circuit has the bake element lltlt) operating at full wattageacross lines L1 and L2 at 240 volts through first switch 50 and itsswitch contacts 54, 54 to the line terminal Lll through switch contactsU2, M3 to load terminal K and through the bake element 100. During theBaking cycle, the other two heating elements 102 and 104 are alsoenergized. They are in a series circuit connected back to first switch5% through contacts 54 and 541 by means of oven selector switch lltlo,terminal Lll through oven switch contacts 118, 119 to load terminal P,and then through the mullion heater MM and the broil element W2.

In the Broiling circuit only the broil element W2 is energized and it isacross lines Ll and L2 through first switch 50 contacts 54 and 54' tooven selector switch terminal Ll through switch contacts 117 and 116 toload terminal I and then through the broil element 102.

Should there be a component failure during an operation of Baking, TimeBaking or Broiling and should the oven temperature rise above the presettempera ture of the oven thermostat 10S and reach an oven temperature ofsay 600 to 650F, then first switch 50 of double-point,thermally-responsive switch ll) would be operated by thermostat 20 toopen the circuits through switch contacts 54, 54', thereby de-energizingthe heating elements and preventing a runaway temperature condition.Thus, first switch 50 of the thermal switch assembly It serves as anover-temperature limit control when the oven is in any normal cookingoperation. In the event of a malfunction of the primary temperaturecontrol, any hazard due to overheating of the oven during the Baking,Broiling and Time Baking mode of operation is eliminated.

Second switch 60 of the thermally-responsive switch assembly 10 isarranged to be in an operating circuit only during the heat-cleaningmode of operation. During the cleaning operation, the three heatingelements 100, 102 and 104 are connected in parallel at half voltageacross line L2 and neutral conductor N in order to obtain a heating ratesomewhat lower than the heating rate of the normal baking operation. Attemperatures belowabout 540F, the switch contacts 64, 64 of secondswitch 60 are in their normally-closed state to allow actuation of doorinterlock solenoid 122. At temperatures above 540F, contacts 62, 62 areclosed to provide the power for cooling fan 11241 which causes air to becirculated between the oven liner wall and the outer oven wall and theouter oven walls so as to keep these outer walls cooled. After atemperature dwell of approximately 10F, or somewhere near 550F,normally-closed contacts 64, 64' of second switch 60 are opened cuttingpower from door interlock solenoid 122, thus preventing the electricalcircuit for the door latch from being actuated. Contacts 62, 62 remainclosed until the interior temperature of the oven drops below 540F. Fora more thorough discussion of the oven door latching environment inwhich the present invention is used, reference is made to US. Pat. No.3,484,858 Jordan et al, assigned to the same assignee as the presentinvention.

In order to set up the heat-cleaning circuit there are severalpreliminary operations that must be performed first. It is imperativethat the oven door first be closed and then locked before theheat-cleaning cycle is initiated, and also that the door remain closedand incapable of being operated or opened while the oven temperaturesare above normal cooking temperatures. A door latch mechanism isactuated by a door lock lever (not shown) and is provided with anautomatic latching means in the form of a spring-biased, pivoted hookmember 125 which latches the door latching mechanism in both its openand closed positions. In other words, the latching means must bedisengaged before the oven door lock lever may be shifted. This isaccomplished by connecting a solenoid 122 across line L1 and neutralconductor N through second switch 60 contacts 64, 64 and then to amomentary latch-release switch 126 and then through the solenoid 122 toswitch contacts 136 and 137 of the selector switch 106. Thus, attemperatures below the operating temperature of second switch 60, thatis below 540F, it is possible to switch the oven door lock lever byclosing the momentary latch releasing switch 126, thereby energizingsolenoid 122 which picks up the automatic locking device and releasesthe door latch mechanism. However, at temperatures above normal cookingtemperatures, that is, above 550F, contacts 64, 64- of second switch 60will be opened thereby disabling the solenoid circuit and preventingaccess to the oven during the heatcleaning cycle. It is not feltnecessary to go into any further detail of the power and control circuitsince the present invention is centered around the double-point,thermally'responsive switch assembly 10 rather than in the overallcircuit and oven combination in which it has been used.

Modifications of this invention will occur to those skilled in this art,therefore, it is to be understood that this invention is not limited tothe particular embodiments disclosed but that it is intended to coverall modifications which are within the true spirit and scope of thisinvention as claimed.

What is claimed is:

l. A multiple point, thermally-responsive switch assembly comprising:

a base;

a housing attached to said base;

a plurality of switch means attached to said housing;

rigid, motion-amplifier'means hingedly attached to said base, saidamplifier means operationally engaging said switch means;

temperature responsive means attached to said base,

said temperature responsive means having a driver; and

a universal motion translator operatively coupled in tension said driverand said amplifier means to further effect opening and closing of saidtemperature responsive means being exposed to predeterminedtemperatures.

2. The invention of claim 1 wherein the temperature responsive means isa thermostat of the differential expansion type having an outer tubesecured to the base and an inner driver secured to the tube at the freeend thereof, the driver being formed of a material having a much lowercoefficient of thermal expansion than that of the outer tube material.

3. The invention of claim 1 wherein the rigid amplifier means is a leverfor transferring motion from said driver to said switch means to effectopening and closing thereof.

4. The invention of claim 1 wherein the universal motion translator is aball and socket joint.

' 5. A double-point, thermally-responsive switch assembly comprising:

a base;

a housing attached to said base;

a pair of switch means attached to said housing;

a rigid, motion-amplifier lever hingedly attached to said base, theamplifier lever operationally engaging said switch means;

a differential expansion thermostat having an outer tube secured to saidbase and an inner rod driver secured to the tube at the free endthereof;

a motion translator of the ball and socket type ope ratively coupled intension said lever with said driver for effecting the opening andclosing of said switch upon said thermostat being exposed topredetermined temperatures;

bias means for compressively maintaining said lever in positive contactwith said motion translator ball;

and calibration means located in said housing individually adjusting thetemperature at which each of said switch means will be caused to beswitched by said lever and, thereby, by said thermostat.

6. The invention of claim 5 wherein a first of said switch means is ofthe normally-closed, single-pole, single-throw type, and a second ofsaid switch means is of the single-pole, double-throw type, adaptedfirst to close a set of normally-open contacts at a calibratablepredetermined temperature, then, after a short temperature dwell, toopen a set of normally-closed contacts while still holding closed thenormally-open contacts.

7. The invention of claim 5 wherein the calibration means is a threadedadjustment at the free end of the driver combined with a nut forming apart of the ball and socket motion translator, and a set screwadjustment for biasing the contacts of one of said switch means.

8. The invention of claim 5 wherein the thermostat driver is formed of amaterial having a much lower coefficient of thermal expansion than thatof the material of the outer tube.

9. A double-point, thermally-responsive, control switch assembly for aself-cleaning electric oven com prising:

an electrically-insulating housing;

a metallic cover for said housing;

a first switch of the normally-closed, single-pole, single-throw type,the switch being secured within said housing;

a second switch of the single-pole, double-throw, rocker-arm type, theswitch being secured within said housing and having first, normally-opencontacts and second, normally-closed contacts;

a rigid, metal, motion-amplifier lever hingedly at tached at a pointoff-center thereof to said cover, the lever having an abutment ofinsulating material located at a free end of the lever further from thehinge point thereof and adapted to operationally engage said first andsecond switches;

a differential expansion thermostat having an elongated outer tubesecured to said base and an inner, rod driver secured to the tube at thefree end thereof, the driver being formed of a material having a muchlower coefficient of thermal expansion than that of the material of theouter tube, the ther- 9 mostat being adapted to project within the ovento switched by said lever and thereby, by said thermosense thetemperature therewithin; stat, including a threaded adjustment at thefree a ball and socket joint motion translator operationd f aid d ivombined with a nut forming a y Coupled in tension Said lever at a freeend part of said ball and socket motion translator, and

nearer the hinge point thereof with the free end of 5 said driver foreffecting the opening of said first Swtch .upon the thermostat beingexposed 10. The invention of claim 9 wherein said first switchdetermined elevated temperatures, and closing of the normally-opencontacts of said second switch, is of the high. Switchblade type adaptdto and after a short temperature dwell, the opening of 0 only at the hpoint the contacts i fm the normally-closed contacts of said secondswitch further havmg f P blas means for mamtammg while holding closedthe normally-open contacts; the 9 Pomts P Y' engagement, and compressivebi means disposed between Said lever wherein said second switch hascompressive bias means and said cover for maintaining said lever inpositive for maintaining Said, normally-Closed Contacts in tight"contact with said motion translator ball; and ly-closed ng g and formaintaining p the calibration means for adjusting the temperature atnormally-open contacts.

which each of said switches will be caused to be a set-screw adjustmentfor biasing said normallyopen contacts of said second switch.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 a 821a 683 Dated June 28 1974 mus Bowlin Inventor(s) 7 Tea g It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 7, line 51, after "tension" insert between Column 8, line 13,"coupled" should read coupling Column 9,

line 4, "coupled" should read coupling Signed and sealed this 24th dayof September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-105O (10-69) uscoMM-Dc Q0376-p59 a U5. GOVERNMENTPRINTING OFFICE: I969 o-aes-zzu,

IINITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 a821 a 683 Dated June 28 a 1974 T mus Bowlin Inventor(s) ea g It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 7, line 51, after "tension" insert between Column 8, line 13,"coupled" should read coupling Column 9,

line 4, "coupled" should read coupling Signed and sealed this 24th dayof September 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. A multiple point, thermally-responsive switch assembly comprising: abase; a housing attached to said base; a plurality of switch meansattached to said housing; rigid, motion-amplifier means hingedlyattached to said base, said amplifier means operationally engaging saidswitch means; temperature responsive means attached to said base, saidtemperature responsive means having a driver; and a universal motiontranslator operatively coupled in tension said driver and said amplifiermeans to further effect opening and closing of said temperatureresponsive means being exposed to predetermined temperatures.
 2. Theinvention of claim 1 wherein the temperature responsive means is athermostat of the differential expansion type having an outer tubesecured to the base and an inner driver secured to the tube at the freeend thereof, the driver being formed of a material having a much lowercoefficient of thermal expansion than that of the outer tube material.3. The invention of claim 1 wherein the rigid amplifier means is a leverfor transferring motion from said driver to said switch means to effectopening and closing thereof.
 4. The invention of claim 1 wherein theuniversal motion translator is a ball and socket joint.
 5. Adouble-point, thermally-responsive switch assembly comprising: a base; ahousing attached to said base; a pair of switch means attached to saidhousing; a rigid, motion-amplifier lever hingedly attached to said base,the amplifier lever operationally engaging said switch means; adifferential expansion thermostat having an outer tube secured to saidbase and an inner rod driver secured to the tube at the free endthereof; a motion translator of the ball and socket type operativelycoupled in tension said lever with said driver for effecting the openingand closing of said switch upon said thermostat being exposed topredetermined temperatures; bias means for compressively maintainingsaid lever in positive contact with said motion translator ball; andcalibration means located in said housing individually adjusting thetemperature at which each of said switch means will be caused to beswitched by said lever and, thereby, by said thermostat.
 6. Theinvention of claim 5 wherein a first of said switch means is of thenormally-closed, single-pole, single-throw type, and a second of saidswitch means is of the single-pole, double-throw type, adapted first toclose a set of normally-open contacts at a calibratable predeterminedtemperature, then, after a short temperature dwell, to open a set ofnormally-closed contacts while still holding closed the normally-opencontacts.
 7. The invention of claim 5 wherein the calibration means is athreaded adjustment at the free end of the driver combined with a nutforming a part of the ball and socket motion translator, and a set screwadjustment for biasing the contacts of one of said switch means.
 8. Theinvention of claim 5 wherein the thermostat driver is formed of amaterial having a much lower coefficient of thermal expansion than thatof the material of the outer tube.
 9. A double-point,thermally-responsive, control switch assembly for a self-cleaningelectric oven comprising: an electrically-insulating housing; a metalliccover for said housing; a first switch of the normally-closed,single-pole, single-throw type, the switch being secured within saidhousing; a second switch of the single-pole, double-throw, rocker-armtype, the switch being secured within said housing and having first,normally-open contacts and second, normally-closed contacts; a rigid,metal, motion-amplifier lever hingedly attached at a point off-centerthereof to said cover, the lever having an abutment of insulatingmaterial located at a free end of the lever further from the hinge pointthereof and adapted to operationally engage said first and secondswitches; a differential expansion thermostat having an elongated outertube secured to said base and an inner, rod driver secured to the tubeat the free end thereof, the driver being formed of a material having amuch lower coefficient of thermal expansion than that of the material ofthe outer tube, the thermostat being adapted to project within the ovento sense the temperature therewithin; a ball and socket joint motiontranslator operationally coupled in tension said lever at a free endnearer the hinge point thereof with the free end of said driver foreffecting the opening of said first switch upon the thermostat beingexposed to predetermined elevated temperatures, and closing of thenormally-open contacts of said second switch, and after a shorttemperature dwell, the opening of the normally-closed contacts of saidsecond switch while holding closed the normally-open contacts;compressive bias means disposed between said lever and said cover formaintaining said lever in positive contact with said motion translatorball; and calibration means for adjusting the temperature at which eachof said switches will be caused to be switched by said lever andthereby, by said thermostat, including a threaded adjustment at the freeend of said driver combined with a nut forming a part of said ball andsocket motion translator, and a set-screw adjustment for biasing saidnormally-open contacts of said second switch.
 10. The invention of claim9 wherein said first switch is of the high current, switch-blade typeadapted to flex only at the hinge point to open the contacts, saidswitch further having compressive bias means for maintaining the contactpoints in tightly-closed engagement, and wherein said second switch hascompressive bias means for maintaining said normally-closed contacts intightly-closed engagement and for maintaining open the normally-opencontacts.